Use rustix instead of direct calls to libc.

Use the [rustix] syscall wrapper crate to factor out error handling and
unsafe system calls. This reduces the amount of unsafe code here, and is
a step towards factoring it out entirely once [`AsFd`] is stabilized and
can replace `AsRawFd` for these kinds of uses.

This does require incrementing the minimum required Rust version to 1.48.
Please feel free to decline this PR if you don't wish to take on these new
requirements.

[rustix]: https://crates.io/crates/rustix/
[`AsFd`]: https://doc.rust-lang.org/stable/std/os/unix/io/trait.AsFd.html

Author: sunfishcode

Diff for: .clippy.toml

@@ -1 +1 @@
-msrv = "1.46"
+msrv = "1.48"

Diff for: .github/workflows/ci.yml

@@ -89,7 +89,7 @@ jobs:
       matrix:
         # When updating this, the reminder to update the minimum supported
         # Rust version in Cargo.toml and .clippy.toml.
-        rust: ['1.46']
+        rust: ['1.48']
     steps:
       - uses: actions/checkout@v2
       - name: Install Rust

Diff for: Cargo.toml

@@ -6,7 +6,7 @@ name = "async-io"
 version = "1.6.0"
 authors = ["Stjepan Glavina <stjepang@gmail.com>"]
 edition = "2018"
-rust-version = "1.46"
+rust-version = "1.48"
 description = "Async I/O and timers"
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/smol-rs/async-io"
@@ -28,7 +28,7 @@ socket2 = { version = "0.4.2", features = ["all"] }
 waker-fn = "1.1.0"
 
 [target."cfg(unix)".dependencies]
-libc = "0.2.77"
+rustix = "0.34.0"
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3.9", features = ["winsock2"] }
@@ -42,7 +42,7 @@ tempfile = "3.1.0"
 
 [target.'cfg(target_os = "linux")'.dev-dependencies]
 inotify = { version = "0.10", default-features = false }
-nix = "0.23"
+rustix = "0.34.0"
 timerfd = "1.1.1"
 
 [target.'cfg(windows)'.dev-dependencies]

Diff for: examples/linux-timerfd.rs

@@ -14,6 +14,7 @@ fn main() -> std::io::Result<()> {
 
     use async_io::Async;
     use futures_lite::future;
+    use rustix::fd::BorrowedFd;
     use timerfd::{SetTimeFlags, TimerFd, TimerState};
 
     /// Sleeps using an OS timer.
@@ -24,7 +25,12 @@ fn main() -> std::io::Result<()> {
 
         // When the OS timer fires, a 64-bit integer can be read from it.
         Async::new(timer)?
-            .read_with(|t| nix::unistd::read(t.as_raw_fd(), &mut [0u8; 8]).map_err(io::Error::from))
+            .read_with(|t| {
+                // Safety: Assume `as_raw_fd()` returns a valid fd; when `AsFd`
+                // is stabilized, we can remove this unsafe and simplify.
+                let fd = unsafe { BorrowedFd::borrow_raw(t.as_raw_fd()) };
+                rustix::io::read(&fd, &mut [0u8; 8]).map_err(io::Error::from)
+            })
             .await?;
         Ok(())
     }

Diff for: src/lib.rs

@@ -525,21 +525,19 @@ impl<T: AsRawFd> Async<T> {
     /// # std::io::Result::Ok(()) });
     /// ```
     pub fn new(io: T) -> io::Result<Async<T>> {
-        let fd = io.as_raw_fd();
+        let raw = io.as_raw_fd();
 
         // Put the file descriptor in non-blocking mode.
-        unsafe {
-            let mut res = libc::fcntl(fd, libc::F_GETFL);
-            if res != -1 {
-                res = libc::fcntl(fd, libc::F_SETFL, res | libc::O_NONBLOCK);
-            }
-            if res == -1 {
-                return Err(io::Error::last_os_error());
-            }
-        }
+        //
+        // Safety: We assume `as_raw_fd()` returns a valid fd. When
+        // `AsFd` is stabilized and `TimerFd` implements it, we can
+        // remove this unsafe and simplify this.
+        let fd = unsafe { rustix::fd::BorrowedFd::borrow_raw(raw) };
+        let flags = rustix::fs::fcntl_getfl(&fd)?;
+        rustix::fs::fcntl_setfl(&fd, flags | rustix::fs::OFlags::NONBLOCK)?;
 
         Ok(Async {
-            source: Reactor::get().insert_io(fd)?,
+            source: Reactor::get().insert_io(raw)?,
             io: Some(io),
         })
     }
@@ -1778,7 +1776,7 @@ fn connect(addr: SockAddr, domain: Domain, protocol: Option<Protocol>) -> io::Re
     match socket.connect(&addr) {
         Ok(_) => {}
         #[cfg(unix)]
-        Err(err) if err.raw_os_error() == Some(libc::EINPROGRESS) => {}
+        Err(err) if err.raw_os_error() == Some(rustix::io::Error::INPROGRESS.raw_os_error()) => {}
         Err(err) if err.kind() == io::ErrorKind::WouldBlock => {}
         Err(err) => return Err(err),
     }